Transponders, which are able to exchange data with a polling device via alternating electromagnetic fields, are suitable for the contactless polling of information stored on a movable data storage medium. The coupling with the electromagnetic fields is performed, at least on the transponder side, preferably via magnetic dipole antennas, especially air core coils or ferrite antennas.
For example, a device for the recognition of objects, especially motor vehicles, in which flat antennas of a polling station are recessed into the ground with their antenna surfaces in parallel to the road surface, has been known from DE 40 39 690 A1. As for the polling device, the transmitting antenna is designed as a rotating spaced loop, and the receiving antenna as a simple frame. The orientation of transponder antennas arranged on the underbodies of motor vehicles is adjusted to the orientation of the polling antennas or to the strength distribution of their field such that on the transponder side, the coils wound as flat coils on a rectangular parallelepiped have horizontal or vertical antenna surfaces standing vertically one on top of another.
An antenna system for arrangement in the outer surface of an airplane, especially as a direction-finding antenna, is described in GB A 719526. In a first embodiment, a winding is wound on a rod made of a material of high permeability and the rod is inserted into a slot of the outer surface of the airplane. According to another embodiment, rods made of a material of high permeability are inserted in depressions of the metallic surface of the airplane and they face with one end a coil array inserted into a window of the metallic surface. Another direction-finding antenna for airplanes, in which a direction-finding antenna consisting of two crossed air core coils is arranged in the metallic surface of an airplane behind a window covered by a dielectric plate, has been known from GB A 2024522. These prior-art arrays for direction-finding antennas for airplanes require that the metallic surface of the airplane be interrupted at the site of the antenna. In addition, there are restrictions concerning the nature of the material of the metallic surface, which shall not be magnetic.
Besides applications with transponders located in an extensively undisturbed environment, e.g., with transponders carried by persons, transponder arrays on electrically conductive, especially metallic surfaces with nonuniform orientation of the transponders and objects with respect to a polling device are of considerable significance, especially in automatization engineering for the identification of objects.